Electrical insulating rod



Aug. 22, 1961 M. H. FINK 2,997,529

ELECTRICAL INSULATING ROD Filed July 14, 1958 2 Sheets-Sheet l Aug. 22, 1961 M. H. FlNK 2,997,529

ELECTRICAL INSULATING ROD United States Patent 2,997,529 ELECTRICAL INSULATING ROD Miller H. Fink, Centralia, M0., assignor to A. B. Chance Company, Centralia, Mo., a corporation of Missouri Filed July 14, 1958, Ser. No. 748,466 7 Claims. (Cl. 174-1'38) This invention relates to electrical insulating rods, and with regard to certain more specific features, to rods of this class useful as electrical linemens operating poles and the like.

Among the several objects of the invention may be noted the provision of rigid insulating rods from which are constructed improved linemens poles, said rods and poles having the characteristics of high dielectric strength and resistance of flash-over, low moisture absorption, satisfactory heat distortion temperature and superior weathering properties; the provision of rods and poles of the class described which are nonshattering and also of high mechanical strength in bending and tension; and the provision of an economical and convenient method of manufacturing such rods and poles. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts which will be exemplified in the structures and methods hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a broken-away side elevation showing one form of the invention employing a cellular core;

FIG. 2 is a view similar to FIG.1, showing another form of the invention without said cellular core;

FIG. 3 is a fragmentary enlarged isometric view showing details of the form of the invention shown in FIG. 1;

FIG. 4 is an isometric view illustrating features of a preferred method of manufacturing the rod; and,

FIG. 5 is a diagrammatic view illustrating said method.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Heretofore, electrical insulating rods for use as linemens electrical insulating poles and the like have been made of expensive clear-grained, seasoned wood expensively treated to prevent absorption of moisture during use, such as would reduce their electrical insulating properties. The required wood needed to be carefully selected to avoid inclusion of imperfections such as knots and the like tending to reduce mechanical and dielectric strength and resistance to flash-over. It has been difiicult to manufacture such a wood product which would be stable and indefinitely retain the desirable properties built into it at the time of manufacture. Moreover, such rods or poles after weathering were subject to possible warping, splitting and the like, if not carefully prepared, and with respect to the present form of rod and pole were relatively heavy.

By means of the present invention, an insulating pole may be constructed which, although light in weight, is mechanically strong and of high dielectric strength, which has low moisture absorption, low heat distortion, and which is not adversely affected by extended weathering.

Referring now more particularly to FIG. 1, there is shown at numeral 1 a dielectric insulating tube having a cellular insulating core 11 made according to one form of the invention, the details of which are shown in FIG. 3. This tube 1 has attached at its end conductive fittings 5 and 7 (FIG. 1). The attaching means may 2,997,529 Patented Aug. 22, 1961 be rivets or the like, such as shown for example at 9. These conductive fittings are representative of a large class of different fittings of the type which may be employed on various types of linemens poles or the like and it is to be understood that other pole fittings in addition to fittings 5 and 7 may be used, attached to the pole between its ends. The core 11 is composed of a light, unicellular material, the purpose of which is primarily to act as a filling to prevent entry of moisture into the inside of the pole and subsequent condensation, which might encourage flash-over of electrical current through the tube.

In FIG. 2 is shown a pole similar to that shown in FIG. 1, except that the cellular element 11 has been omitted, as may in some cases be desirable.

Referring now to FIG. 3, the type of insulating rod for the form of the pole illustrated in FIG. 1 is shown in detail. This rod is constituted by the cylindrical core 11 composed of a solidified unicellular thermoplastic or thermosetting foam resin such as, for example, (1) of the polystyrene type sometimes sold under the trade name of Styrofoam, (2) the polyurethane type or (3) of the cellulose acetate type. By unicellular is meant that the foam-formed cells or bubbles in the material are essentially individually closed and discrete, so that the material will not substantially transmit moisture through it. Further description of this material will be unnecessary, since it is available in various shapes, including the solid cylindrical shape illustrated at the right in FIG. 3.

Surrounding the unicellular rod 1 1 are compacted axially laid glass rovings 13, impregnated with solidified thermoplastic or thermosetting resin surrounding their constituent glass fibres. The resin in its rigid state adheres the fibres and attaches the rovings 13 to the rod 11. Any of various appropriate thermoplastic or thermosetting resins may be employed, such as polyester, vinyl, acrylic or epoxy resins. A particularly useful one is an anhydride amine epoxy resin.

Wrapped about the compacted layer 15 of axial roving 13 is a second layer 17 of helically applied compacted glass fibre roving 19, impregnated and attached to layer 15 with the same adhesive material. This helically applied roving is also compacted. As will be shown below, the roving 19 is applied in multiple strands.

Covering the layer 17 is another layer 21 of axially applied compacted glass fibre roving 23 which is also impregnated with said resin. Wrapped around the layer '21 is a Woven-glass tape 25, the successive loops of which overlap. As the layer 26 of tape 25 is applied, it acts as a containment for layer 21 to which it adheres, as well as adhering to itself by said resin, as will be shown. Wiped onto the glass tape layer 26 is a finished coat of said thermosetting or thermoplastic material, as indicated at 27.

In FIGS. 4 and 5 are illustrated the method of organizing the various elements above-described. At numeral 29 (FIG. 5) is shown a basin for a supply pool 31 of said thermoplastic or thermosetting resin, as the case may be. This resin ultimately forms the solidified matrix for impregnating the rovings -13, 19 and 23 and joining them with one another and with the core 11. For purposes of further description, assume that a thermosetting resin is employed. Associated with the basin 29 is a suitable closely fitting inlet guide 33 for the introduction of the preformed rod 11. Within the basin is located a positioning guide 35 for the roving 13. This guide 35 has an opening 37 through which the unicellular rod 11 may pass while moving to the left. Surrounding this opening is a series of guide openings 39 for guiding the roving 13. Each of these openings receives one length of fibre glass roving 13 from a suitable spool of the same (not shown). Toward the other end of the basin 29 is a bundling and squeeze-out die 41 having an opening 43 admitting the unicellular rod 11 and compressively admitting the axially directed fibre glass roving '13 so as to compact them. As shown, the rovings move from the relatively widely spaced guide openings 39 at relatively larger distances from the center of rod 11 into close compressed proximity within the smaller opening of the die 41. Thus, as the solid unicellular rod 11 and the spaced rovings 13 move from member 35, the resin in the basin 2% wets the rovings 13 and impregnates their fibres, while wetting the surface of the rod it. Then the hole 43 in the die 41 squeezes the rovings together against the rod 11, the roving being compacted. The resin material is forced into the interstices between the glass fibres constituting the roving and acts as a binder therefor as well as adhering the roving to the rod 11. The outside surface of the compressed roving which leaves the die 41 is wet with the resin.

Next, several (four in the present case) adjacent fibre glass rovings 19 are wrapped onto the outside of the axial layer '15. The number is variable and in one instance eight have been used. Any known type of planetary helical wrapping means may be employed, and requires no further description. The helically wrapped assembly then moves through a closely fitting inlet 47 of a second basin 49 infilled with an additional pool of said resin 31. In this second basin 49 is a second positioning guide 51 having an opening 53 therein admitting the partially wrapped assembly therethrough. Surrounding the opening 53 on relatively large radii is a circle of roving guide openings 55 for the fibre glass rovings 23, each of which comes from a suitable spool (not shown). The resin 31 impregnates the helically applied roving 19 and also the axially applied roving 23. Then the assembly moves through a second bundling and squeezeout die 57 in which is an opening 59 adapted to squeeze and compact the axially applied roving 23 against the helically applied roving 19. The resin here also is forced into the interstices between fibres of the rovings 23 and 19. As the resulting material leaves the die 57, all of the rovings '13, :19 and 23 of the layers 15, 17 and 21 have had their glass fibres impregnated and compressed, the successive layers have been adhered to one another, and layer has been adhered to rod 11. The surface of layer 21 is then wet with the liquid resin.

The term roving as used herein means a loosely spun yarn of the dielectric fibres selected, preferably glass, which is adapted (after laying up and impregnation as described) to be compacted, whereby the fibres are forced into close proximity Within the plastic matrix left after squeezing while immersed.

After the rod-like material thus combined leaves the die 57, it is wrapped with the containment ribbon of woven glass tape 25. The glass tape absorbs a sui'licient amount of the resin on the surface of layer 21 to effect its impregnation. Under some circumstances it may be desirable that this tape shall have been resin-impregnated prior to the time of its application. However, the tape may be for containment purposes only and composed, for example, of cellophane.

After application of the woven tape 25, the entire assembly is passed through a heating oven (not shown) operating at a suitable curing temperature, for example, in the case of an anhydride amine epoxy resin, at a temperature of 100 C.120 C. This cures or sets and hardens the resin. Curing occurs at region 0, which has been foreshortened for convenience in FIG. 5. Next the surface of the glass tape is circularly ground in order to move irregularities and to provide a smooth cylindric form, or, particularly in the case of cellophane tape, may be removed entirely by grinding or sanding. Grinding or sanding occurs at region G, which is also foreshortened. Then a coating of, for example, a liquid thermoplastic resin 27, such as above described, is applied with a wipe finish over the layer 26 formed by the helical glass tape 25. This occurs at C. This resin is preferably of a type which will cure and harden at room temperature.

Movement of the material from right to left, as illustrated in FIG. 4, is accomplished by suitable draw rolls (not shown) operating on the finished product in the usual manner as it emerges from the process. Beyond the draw rolls, the rod is cut into appropriate lengths for manufacture of a pole such as illustrated in FIG. 1. It will be understood that if it is desired to color the rod, a suitable die may be incorporated at any stage with the applied resin.

The heating, grinding, coating, draw-roll and cutting means are each per se conventional and therefore are not illustrated. Some resins employing curing catalysts may be cured by air drying at room temperatures, in which case oven heating such as at 0 may be dispensed with. It is to be understood that different types of resins may be used in the basins 29 and 49, respectively.

The form of pole illustrated in FIG. 2 is produced by substituting a metal rod or mandrel for the unicellular core 11 used in the process described (FIG. 4). In this case, the mandrel extends through the basins 29 and 49 to an appropriate point toward the left at which it is safe to have the resulting tube interiorly unsupported by the mandrel as, for example, to the point of entry into the oven or extending through the oven to its point of exit. The exact point depends upon the character of the resin employed as respects its affinity for adhering to the surface of the mandrel. In other words, the material is permitted to be drawn from the surface of the stationary mandrel before it reaches any condition wherein it tends to adhere strongly to the surface. To discourage such adherence, the mandrel should preferably be of metal and have a smooth surface. The mandrel and the unicellular core 11, insofar as the process is concerned, have similar functions, namely, to form a cylindric surface upon which the axially disposed rovings 13 are laid. In the case of the core 11, it is left in place, but in the case of the mandrel, it is in effect continuously withdrawn as the rod which is being formed is pulled away from it.

The rod obtained by forming it over and withdrawing it from a mandrel as above described is useful for the form of the invention shown in FIG. 2, wherein the pole is hollow. This form of the rod may be used under circumstances wherein the fittings attached to the tube 1, such as 5, 7 and others, enclose the ends of the rod and are installed with a suitable sealing mateiial such as an epoxy adhesive, which will hermetically seal and prevent entry of moisture into the resulting pole. By this procedure, entry and circulation of air through the rod are prevented, as well as condensation of moisture therein. The fittings 5 and 7 shown in FIG. 2 comprise cup-like enclosing heads 61, the sealant being shown at 63. The same kind of sealant is used in setting the rivets 9.

The form of the invention shown in FIG. 1, including the unicellular core 11, has the advantage that the pole fittings 5 and 7 require no sealant for their application. The advantage of the form of the pole shown in FIG. 2 is that it is lighter by reason of the absence of unicellular core 11, requiring, however, that the sealant for the fittings 5, 7. An acceptable density of the unicellular core 11 is four to six pounds per cubic foot, which results in additional weight in the form of the invention shown in FIG. 1 of merely a few ounces for the normal size of pole. Thus the amount of weight of unicellular material in a 10-foot pole having approximately a 1-inch inside diameter may be on the order of four to six ounces. The wall thickness of either form of pole shown in FIGS. 1 and 2, exclusive of the core 11 shown in FIG. 1, is small, being on the order of inch or so for smaller diameters and may be on the order of inch or so for larger diameters.

It will be understood that while the materials mentioned above are preferable for obtaining the improved results set forth, others may be employed whose electrical properties, weathering properties, moisture-absorption properties and heat distortion are satisfactory for the electrical applications set forth.

The term roving is used herein in the usual sense that the material of which it is composed is only slightly twisted, which leaves it in a comparatively soft and highly absorptive state toward liquids such as the uncured resin 31. Improved surface absorption is thus operative and in the case of rovings 13 and 23 even more so because of the individual immersion of each rove or roving as it enters its respective pool 31 and before it reaches contact with the core 11. Moreover, the core 11 is individually wetted by the resin before any roving reaches it. It will also be noted that the squeezing forces at 43 and 59 on the comparatively soft roving exert themselves primarily in squashing the roving Without engendering large radial forces which otherwise would tend to collapse the foam-like surface of the core 11, which is relatively fragile until the final formation of the cured tube 1 around and attached to it forms a stiff protective casing therefor.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A substantially rigid dielectric pole, comprising a cylindrical core of solidified unicellular plastic dielectric material adapted to prevent passage of moisture therethrough, a compact layer of axially disposed compressed fibrous rovings of a dielectric material closely surrounding said core, a compact layer of helically disposed compressed fibrous rovings of dielectric material closely surrounding said axial rovings, a compact layer of axially disposed compressed fibrous rovings of a dielectric material closely surrounding said helically disposed rovings, and a solidified dielectric thermoset plastic in and around the rovings forming a matrix for their fibres and connecting the rovings to one another and to the core to form a hermetic seal between said core and said solidified dielectric plastic.

2. A pole according to claim 1, wherein the fibrous rovings consist of glass fibres.

3. A pole according to claim 2, wherein said solidified unicellular plastic is composed of a polyurethane foam.

4. A pole according to claim 2, wherein said solidified unicellular plastic is composed of a polystyrene foam.

5. A pole according to claim 2, wherein said solidified unicellular plastic is composed of cellulose acetate foam.

6. The method of constructing rigid dielectric rods comprising immersing and axially moving a core of solidified dielectric unicellular foam resin in a pool of liquid dielectric plastic which is ultimately adapted to be hardened by curing, immersing rovings of fibrous dielectric material in said pool separate from the core for unobstructed surface application of the resin to the surface of the core, and to the rovings for thorough absorption thereby, moving the rovings into engagement with said moving core, peripherally squeezing the immersed rovings adjacently to the immersed surface of the core as the core moves to compact the rovings and engage them with the core to form a first adhered plasticimpregnated layer of rovings on the core, applying additional rovings of fibrous dielectric material on said first layer to form a second layer around the first layer as the core moves, immersing and axially moving the core with the applied first and second layers in a pool of said dielectric material, immersing in the last-named pool additional rovings of fibrous dielectric material separate from the second layer for unobstructed surface application of the resin to the second layer, and unobstructed surface application to said additional rovings for thorough absorption thereby, peripherally squeezing the immersed third and second layers of rovings to compact them closely around the first layer to form plastic-impregnated first, second and third compacted layers adhered by a plastic matrix with one another and with the core, and curing the plastic matrix to solidify it.

7. The method of constructing rigid dielectric rods comprising immersing and continuously axially moving a continuous core of solidified dielectric unicellular foam resin in a pool of liquid dielectric plastic which is ultim'ately adapted to be hardened by curing whereby the core surface is completely covered with plastic, immersing rovings of fibrous dielectric material in said pool separate from the core for separate application of the resin to the rovings and axially moving them along with and into closely adjacent parallel engagements with said moving core while immersed, peripherally squeezing the immersed rovings around the immersed surface of the core as the core moves to compact the rovings to form an attached first plastic-impregnated layer on the core, wrapping rovings of fibrous dielectric mate-rial around said first layer to form a helical second layer around the moving core, axially immersing and moving the core with the applied first and second layers in a pool of said dielectric material, immersing additional rovings of fibrous dielectric material in the latter pool separate from the second layer for separate application of the resin to the additional rovings, axially moving the last-mentioned rovings into axial engagement over said second layer while moving and immersed in order to form an impregnated third layer of parallel rovings of fibrous dielectric material on the second layer, peripherally squeezing the immersed third layer of rovings to compact them and the second layer around the first layer to form plastic impregnated parallel first, helical second and parallel third compacted layers adhered by a plastic matrix with one another and with the core, curing the plastic matrix to solidify it, and cutting said continuous core into lengths.

References Cited in the file of this patent UNITED STATES PATENTS 1,717,287 Warren et al. June 11, 1929 2,438,504 Hubbard Mar. 30, 1948 2,625,498 Koch Jan. 13, 1953 2,723,705 Collins Nov. 15, 1955 2,741,294 Pancherz Apr. 10, 1956 2,814,666 Maddox Nov. 26, 1957 FOREIGN PATENTS 627,255 Great Britain Aug. 4, 1949 781,473 Great Britain Aug. 21, 1957 1,145,447 France May 6, 1957 215,188 Australia May 21, 1958 OTHER REFERENCES Publication: 3 New Foams, Modern Plastics, April 1953, pages -87.

Publication: Thielman: Foamed Plastics for Structural Functions in Electronic Equipment, reprinted from the January 1958 issue of Electrical Manufacturing, 7 pages. Page 7 relied on. 

1. A SUBSTANTIALLY RIGID DIELECTRIC POLE, COMPRISING A CYLINDRICAL CORE OF SOLIDIFIED UNICELLULAR PLASTIC DIELECTRIC MATERIAL ADAPTED TO PREVENT PASSAGE OF MOISTURE THERETHROUGH, A COMPACT LAYER OF AXIALLY DISPOSED COMPRESSED FIBROUS ROVINGS OF A DIELECTRIC MATERIAL CLOSELY SURROUNDING SAID CORE, A COMPACT LAYER OF HELICALLY DISPOSED COMPRESSED FIBROUS ROVINGS OF DIELECTRIC MATERIAL CLOSELY SURROUNDING SAID AXIAL ROVINGS, A COMPACT LAYER OF AXIALLY DISPOSED COMPRESSED FIBROUS ROVINGS OF A DIELECTRIC MATERIAL CLOSELY SURROUNDING SAID HELICALLY DISPOSED ROVINGS, AND A SOLIDIFIED DIELECTRIC THERMOSET PLASTIC IN AND AROUND THE ROVINGS FORMING A MATRIX FOR THEIR FIBRES AND CONNECTING THE ROVINGS TO ONE ANOTHER AND TO THE CORE TO FORM A HERMETIC SEAL BETWEEN SAID CORE AND SAID SOLIDIFIED DIELECTRIC PLASTIC. 